Radio-frequency identification (RFID) in its various configurations is a widely used technology and well known in the art. This technology is so widely used in many applications that RFID tags need to be produced at very low cost and ideally consume minimal power. This can result in a restricted reading range.
Currently, RFID systems operate mainly at frequencies below 2.4 GHz. The relatively long wavelength means that practical antenna structures are electrically small and no significant directivity can be achieved. The systems either read all tags within a certain range or some kind of addressing scheme is needed.
Current RFID technology currently uses an addressing scheme that operates via reading unique identities of one or more RFID tags (or other such radio frequency signalling sources). If a user wishes to read a particular tag via selective reading, an RFID reader presently known in the art will set up an electromagnetic field for reading RFID tags (or other such radio frequency identification sources). All tags within that field then respond to the reader indicating their own unique identity. Once the RFID reader has determined the identities of each transmitting/responding RFID tag, the reader then instructs each tag in turn to transmit in isolation until it identifies the particular source it is interested in. After this point, communication between the RFID tag of interest and the RFID reader can begin.
With current RFID systems, selective tag reading can only be done from a very short distance (as in near-field-communications, NFC) or by using pre-existing information about the tag (identification by address code etc). The tag identity cannot be directly linked to its location when several tags are read.
P. Pursula, T. Vaha-Heikkila, A. Muller, D. Neculoiu, G. Konstantinidis, A. Oja, J. Tuovinen, “Millimeter-Wave Identification—A New Short-Range Radio System for Low-Power High Data-Rate Applications,” IEEE Transactions on Microwave Theory and Techniques, Volume 56, Issue 10, pp. 2221-2228, October 2008 discusses the use of millimeter waves with RFID technology (for example, using low-power or passive backscattering tags for short-range high data rate applications).
A directive antenna beam, such as those achieved using millimeter wave frequencies can help in selective reading of a single tag. However, even with millimeter-wave antennas, practical and technological issues present in the art limit radio frequency identification systems to a level that does not entirely eliminate co-channel interference when the unwanted tags transmit within range.
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